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3.4.8 Procedure for lowering blank value of collector tube
Before using the collector tube, heat-treat it using an electric furnace* or the like to lower
the blank value, and keep it in an airtight container.
Since dirt before and after the collector tube also affects a measurement, we recommend
the heat treatment of the whole pipe.
Clean the container to keep collector tubes and rubber
plugs referring to the previous section.
Wipe off dirt on collector tubes. Wipe the inside using a
swab or the like soaked with a little ethanol.
Put the collector tubes on a heat-resistant alumina pan or
the like, and heat them at 800
°
C for 30 minutes or more
using an electric furnace.
* Take care because quartz tubes may break easily
because of devitrification if sodium, calcium or the like
adheres to them.
When the temperature in the electric furnace has lowered
and it is possible to take out the quartz tubes, take them
out using a flat trowel, tongs or the like while protecting
yourself using heat-resistant gloves etc., and cool the
quartz tubes.
* Take sufficient care not to receive a burn, and follow the
instruction manual of the electric furnace when taking out
the quartz tubes.
* If a heat-resistant alumina pan is cooled rapidly, it may
break.
When the quartz tubes have been cooled to 50
°
C
or less,
put them in a case as soon as possible.
* If they are left intact for a long time in a room, they may
adsorb mercury in the environment and blank values may
increase.
Conduct a sampling inspection and check a blank value.
(An inspection of one or more out of 10 quartz tubes is
recommended.)
Do not use a collector tube that has discolored wool after the heat treatment. The
capability to collect mercury may have decreased.
